E. coli is a member of the Enterobacteriaceae, or enteric bacteria, which are Gram-negative microorganisms that populate the intestinal tracts of animals. Other members of this bacterial family include Enterobacter, Klebsielia, Salmonella, Shigella and Yersinia. Although E. coli is found normally in the human gastrointestinal tract, it has been implicated in human disease, including septicaemia, meningitis, urinary tract infection, wound infection, abscess formation, peritonitis and cholangitis.
The disease states caused by E. coli are dependent upon certain virulence determinants. For example, E. coli has been implicated in neonatal meningitis and a major determinant of virulence has been identified as the K1 antigen, which is a homopolymer of sialic acid. The K1 antigen may have a role in avoiding the host's immunological system and preventing phagocytosis.